2.4 GHz vs. 900 MHz Phone Technology

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Dean Huster
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2.4 GHz vs. 900 MHz Phone Technology

Post by Dean Huster » Tue Jul 01, 2003 3:45 pm

We just bought a $25 2.4GHz phone from Sam's. We live on a square 10-acre acreage and with the 900 Mhz phone, I can hit the dial tone and talk anywhere on the property. With the newer 2.4 GHz phone, there are some places where I can't even get more than 50 feet away from the base unit without losing contact. What gives? I thought that the 2.4 GHz technology was supposed to be so wonderful. Does it really have less range than the 900 MHz band and manufacturers only use the higher band because there may be more channels available or something? About the only advantage I've seen so far is that there won't be any interference between the two cordless phones.<p>I'm not well-informed on this technology. Do I have a lousy 2.4 GHz phone (GE, "Brings good things to " something) or is this a normal expectation?<p>Dean
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IRONMAN
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Re: 2.4 GHz vs. 900 MHz Phone Technology

Post by IRONMAN » Tue Jul 01, 2003 7:37 pm

I don't know a whole lot about the newer rf technologies, but I allways assumed frequencys in the GHZ range would travel further(at least line of sight.).
To be honest, after having known and talked to several "engineers" , some of whom could'nt even build an audio freq. amp for thier guitars, I'm truly suprised anytime something electronic works at all.
It seems to me that most of the people in the field today learn to use "functional blocks", and have VERY limited understanding of the foundations.
Earlier I posted asking for opinions on favorite books(I think you also responded.), if you go through the list(I don't want to know how much money that idea cost me, amazon likes me right now though.), you'll notice that most of the titles are rather dated. Even so they are still superior to anything recent. Thats a sad statment.<p>Regards;
Shelby.

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Re: 2.4 GHz vs. 900 MHz Phone Technology

Post by Mike » Tue Jul 01, 2003 7:43 pm

It could be your 'lousy' GE phone, but most likely not. If you have a wireless LAN set up at your home, that is most likely the problem. Wireless LANs run on the same 2.4ghz frequency. They can cause problems with the phone, and the same is true that the phone can interrupt the lan. Also, look on the box for the phone. I'm pretty sure that it doesn't say anything about longer distances. It just says that 2.4ghz brings up clarity. Other devices could cause the problem also, such as a nearby TV, Radio, Flourescent Lamp, etc. I would suggest purchasing a 5.8ghz phone, instead of using your 2.4ghz. Best Buy sells them for cheap. for some reason, though, www.bestbuy.com presents you with a message saying something about their site under construction. I figured out that going to www.bestbuy.com/index.html gets you into the site.<p>-Mike

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Re: 2.4 GHz vs. 900 MHz Phone Technology

Post by bodgy » Tue Jul 01, 2003 8:34 pm

The 2.4GHz phones are mainly line of sight, no hills no trees waving in the wind. The claims of them having a range of 1-10Klm's is worked out under lab conditions and then the marketing dept. gets its hands on the specs.<p>Is this phone a 'true' 2.4GHz ? By that I mean is it like the Panasonic offering that has two aerials that operate similar to the old 1200/75 baud modem system.These phones transmit between base and reciever at 2.4GHz and receive at 900MHz<p>If these phones are DECT ones then you should get better range as these work on a digital broadcast signal.<p>The non DECT ones can still have their range shortened if they are molested by fluorescent lighting, poor power supply hum shielding and even poorly shielded mains building runs.<p>It may )if the phone was cheap) be worth opening it up and checking the quality of the solder joints - many phones out of Malaysia and China often have poor joints mainly around the aerial connection and speaker terminals.<p>In my experience the best quality control comes from the Uniden factory in China - however this only works for their own phones. The other brands names they sometimes produce do not get the same QC checks. Doro phones vary in quality depending on whether they are the Doro designed range or the leftover Audioline products.<p>If the phones are made by Alcatel, Philips or Ericsson then the European manufactured ones seem more reliable then the Singapore/Malaysia based ones.<p>Colin
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Re: 2.4 GHz vs. 900 MHz Phone Technology

Post by analogee » Tue Jul 01, 2003 10:11 pm

We've got a Siemens 2.4 GHz phone, but never had a 900 MHz to compare with it. It is "spread spectrum", which I guess implies it is digital transmission, although one could make a case for saying that any wideband FM transmission is "spread spectrum". Spread spectrum should be more robust in the presence of interfering signals.<p>Anyway, it just barely covers inside the entire house, sometimes breaking up a bit, but usable. Outside, in the shop building, it is reliable, but the distance from the base station is only about 30 or 40 feet.<p>So, I guess I'm saying your 50 ft. experience pretty much correlates with what we're getting here with our phone; I can't stay reliably connected over our entire 1.7 acre property. And I always thought Siemens was a good brand (German can't be bad, right?).<p>I'm not much of an RF guy, so correct me if I'm wrong, but I don't see why 2.4 GHz would be inherently better than 900 MHz. Aren't short wavelengths more likely to be disrupted by smaller obstacles, to put it very crudely? On the other hand, I've used 900 MHz walkie talkies (with more power, I'm sure) that could easily cover distances of thousands of feet.<p>I believe the 2.4 GHz selection has to do with licensing issues, and the relatively vast bandwidths available up there so they can get away with spraying our stupid phone conversations over multiple MHz of spectrum space. I'm also guessing that they backed off on the transmit power considerably, making use of the digital communications capability, and ended up making something that actually works a little worse than the old technology, but is adequate for the vast majority of users, is lighter, cheaper (eventually), and smaller. But that's all just a guess.<p>Regards,
Todd
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Dean Huster
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Re: 2.4 GHz vs. 900 MHz Phone Technology

Post by Dean Huster » Wed Jul 02, 2003 5:10 am

It's pretty hard to find non-digital phones anymore. Oour 900 MHz phone is "spread spectrum" which is usually there to imply some kind of frequency-agile technology where the phone system will hop around in frequency either for selecting a channel with the best comm characteristics or to help "encode" the conversation and make it harder for an outsider to "hear", although the digital technology pretty much takes care of that with regard to the use of scanners.<p>Yeah, as you go up in frequency, you get more of a line-of-sight operation and absorption and blockage by large objects becomes a problem. But that would imply that the signal wouldn't go through walls from room to room, wouldn't it?<p>I'd heard of reports that a 900 MHz phone signal could sometimes reach out a couple of miles under good conditions.<p>Is this a full 2.4 GHz phone vs. one that's duplexed over two bands? I think so. Had to open it up the other night to drain the water from the base unit after dumping a glass over on it during the night (the poor reception was long before this, folks!) and when I had it open I noticed that the little nubby on the top edge that I was assuming was some kind of a little snubby antenna is nothing more than a plastic decoration. The actual antenna is a couple of 1-inch "springs" inside the base unit.<p>I really hate technology when it's produced solely for technology's sake ... e.g., a 758-function scientific calculator, a CD player with a 79-button remote, a 36-button car stereo, etc.<p>Dean
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bodgy
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Re: 2.4 GHz vs. 900 MHz Phone Technology

Post by bodgy » Wed Jul 02, 2003 5:41 am

And when I was in my early teens I thought 8 -tracks, were to die for!<p>
Phones don't have to be DECT to be spread spectrum.<p>The US models are different to the European/Aus/NZ models in their specs especially in the number of channels - I believe 100 is more or less standard in the US. Aus only allows 10 much to Unidens and Ericssons annoyance.<p>Somewhere there is an Ericsoon/Siemens site with all the specs for DECT - GM (Holden) not so long ago had the all in one mobile/DECT system for using in the factory grounds.<p>A website for those interested http://searchnetworking.techtarget.com/ ... 89,00.html<p>Colin<p>[ July 02, 2003: Message edited by: bodgy ]</p>
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Edd
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Re: 2.4 GHz vs. 900 MHz Phone Technology

Post by Edd » Wed Jul 02, 2003 11:13 am

Dean:
I was just going to suggest what I always do in that situation.Utilizing a bit of the premium low loss coax and the utilization of a hand fabbed extension antenna on the base unit. . Just think, at this site, the unknowledgeable person could. even spend more for one than your phone cost !!!
http://www.twacomm.com/Catalog/Jmp_Wint ... t_ID_8.htm <p>73's de Edd
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by Comcast…more apropos would be:
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Re: 2.4 GHz vs. 900 MHz Phone Technology

Post by myp71 » Sat Jul 12, 2003 10:09 pm

The 2.4ghz phones have to be digital and a lot of them are not trust me I'm phone shopping or trying to.<p>
Myp71

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Re: 2.4 GHz vs. 900 MHz Phone Technology

Post by josmith » Sun Jul 13, 2003 10:45 am

Some 2.4 ghz phones say on the box that they are analog some say DSS and some don't commit. I've never owned one and after reading this thread I'm in no hurry to try one.<p>What is DECT ?<p>I've heard that FM radio (88-108 mhz) is line of sight and when i studied air navagation the freguencies they used were just above FM broadcast band and were considered to be line of sight. <p>We use 460 mhz radios where i work and they go through steel buildings,wood buildings brick walls and large castings.<p>900 mhz phones have similar capabilities. <p>So it seems that the expression "line of sight " is meaningless.

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Re: 2.4 GHz vs. 900 MHz Phone Technology

Post by rshayes » Sun Jul 13, 2003 5:01 pm

"Line of sight" frequencies are generally those above about 40 to 50 megahertz. Under normal conditions, transmissions on these frequencies do not propagate much beyond the visible horizon. Additional range can be obtained by putting the antenna on a tall structure, which can extend the "line of sight". Under abnormal conditions, such as atmospheric ducting of various kinds, "line of sight" frequencies can go farther. Amateur communications have taken place between California and Hawaii on frequencies at least as high as 450 MHz and possibly higher. This took months of waiting until a "duct" formed between those two points. Other exceptional cases occur when the sunspot cycle is at its maximum. Occaisionally TV signals from the Midwest show up in California. Normally, the visible horizon is about the limit, however.<p>Cordlesss phones are intended to be limited in field strength so that they will not be detectable at any great distance. Most unlicensed uses of the spectrum are regulated by the FCC by limiting field strength. (Usually Title 47, Part 15 of the Code of Federal Regulations.) The transmitter is regulated, but the receiver is not, so a good receiver with a directive antenna can extend the range quite a bit.<p>There is probably not a theoretical reason for the performance of the 2400 MHz system to be poorer, but there may be practical reasons. The efficiency of transistors falls off quite rapidly with frequency, so the 2400 MHz transmitter may be putting out less power, limited by the battery pack used rather than FCC regulations. The noise figure and gain of the receiver may also be poorer, since these also get worse at higher frequency. Both frequencies may pass through non-metallic building walls, but the attenuation at 2400 MHz is probably higher. I would be rather suprised if the 2400 MHz system did work as well as the 900 MHz system, especially if the cost is about the same.<p>[ July 13, 2003: Message edited by: stephen ]</p>

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Chris Smith
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Re: 2.4 GHz vs. 900 MHz Phone Technology

Post by Chris Smith » Sun Jul 13, 2003 6:03 pm

Dean, watt for watt, the lower the freq, the further it goes. AM is the perfect example, Ham even better. Skip makes it travel. The phones in Question [2.4] lower the power output because of the high freq, knowing its in the house and doesn’t mater. The 900 MHz phones to date have the highest wattage per see, and travel the furthest. However, if you don’t tweak your surroundings too much, add in a 100 milli watt transistor into your phones ant, [plus power] and receive all your calls in the next state? Cost, about 10 bucks? Four wire, and that it. [not legal?]

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Re: 2.4 GHz vs. 900 MHz Phone Technology

Post by bodgy » Sun Jul 13, 2003 8:04 pm

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by josmith:

What is DECT ?<p>
<hr></blockquote><p>Digital Enhanced Cordless Telecommunications<p>for all the info click on the link on my post above.<p>Colin<p>[ July 13, 2003: Message edited by: bodgy ]</p>
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Dean Huster
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Re: 2.4 GHz vs. 900 MHz Phone Technology

Post by Dean Huster » Tue Jul 15, 2003 9:27 pm

Chris, I'm not sure that the lower-the-freq-the farther-the-reach-per-watt theory is entirely accurate. A ham can work around the world with 15 watts on 10 meters during the peak in the 11-year sunspot cycle while KMOX is normally limited to North America east of the Rockies on a good night with its "50,000 red-hot watts".<p>Dean
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Re: 2.4 GHz vs. 900 MHz Phone Technology

Post by rshayes » Wed Jul 16, 2003 6:45 am

Dirrerent rules apply in different cases. Frequencies below the broadcast band are usually considered to be propagated by "ground wave", where much of the path attenuation is due to interreaction with the earth's surface. Both transmitting and receiving antennas tend to be a small fraction of a wavelength and inefficient. Atmospheric noise is high.<p>The broadcast band tends to be ground wave propagation during the day and skip propagation during the night. Transmitting antennas are usually about 1/4 wavelength, which gives moderate efficiency when combined with an elaborate ground system. Receiving antennas are still inefficient, usuall small loop antennas of some form. Atmospheric noise is still high.<p>Above the broadcast band up to about 15 MHz the propagation is often a fairly low loss skip path, antennas are moderately efficient, and atmospheric noise is decreasing. During a sunspot maximum, skip propagation may occur up to 50 or 60 MHz.<p>Once you above 30 MHz, consistant paths are usually line of sight, with some sporadic paths due to ducting effects. The noise level is usually close to thermal noise and independent of frequency. Directive antennas are easy to build and can sometimes be used to increase range. Generating high power becomes more difficult above about 100 MHz and low receiver noise figures are harder to get above about 1 GHz.<p>Somewhere above 20 GHz, water in the atmosphere begins to absorb signals, and the attenuation of even line of sight paths becomes high.<p>In your case, about 100 milliwatts, into a poor antenna, over an obstructed path, with a poor receiving antenna, with a moderate noise figure in the receiver, gives you a range of possibly 100 feet.<p>Now look at a spacecraft. A few watts, at about the same frequency, using a moderate transmitting antenna (2 foot parabola?), over a line of sight path, using a large receiving antenna (150 foot parabola?), and a good receiver (fractional db noise figure) give a range of about 200 million miles.<p>Except for skip or ducting types of propagation, frequency itself is not a strong factor. Higher frequencies may allow higher gain antennas, but these antennas are very directive and not very useful for wireless telephones. Lower frequencies will be a little better simply because better transmitters and receivers can be built for the same cost and with the same power consumption.<p>[ July 16, 2003: Message edited by: stephen ]</p>

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